Scalable Freeform Optimization of Wide-Aperture 3D Metalenses by Zoned Discrete Axisymmetry

We introduce a novel framework for the design and optimization of 3D freeform metalenses that attains nearly linear scaling of computational cost with diameter by breaking the lens into a sequence of radial “zones” with n-fold discrete axisymmetry, where n increases with radius. This allows vastly more design freedom than imposing continuous axisymmetry while avoiding the compromises of locally periodic approximation or scalar diffraction theory. Using a GPU-accelerated finite-difference time-domain solver in cylindrical coordinates, we perform full-wave simulation and topology optimization within each supra-wavelength zone. We validate our approach by designing millimeter- and centimeter-scale polyachromatic, 3D freeform metalenses, which outperform the state-of-the-art. By demonstrating the scalability and resulting optical performance enabled by our “zoned discrete axisymmetry” and supra-wavelength domain decomposition, we highlight the potential of our framework to advance large-scale metaoptics and next-generation photonic technologies.